Laminated glass is a type of safety glass designed to allow glass to shatter, but not break. This is accomplished by sandwiching a bonding agent, often polyvinyl butyral, between two layers of glass. The bonding agent holds the glass together even after it has shattered.
First used in the eye-pieces of gas masks in World War I, laminated glass is now widely used as auto windshield glass, and can be recognized by its characteristic “spider-web” shatter. Such glass is used in places that a manufacturer believes there is a possibility of human impact on the glass or when the glass is placed in such a way that if broken, it could fall and cause harm. Skylights, for example, are also made with laminated glass.
Before 1939 when Ford Motor Company began using a laminated glass in its vehicles known as “Indestructo,” this type of glass was not widely used due to the various problems and concerns it caused, including its tendency to become discolored. But once the usefulness and strength of laminated safety glass became apparent, it replaced non-laminated glass in motor vehicles.
How Its Made
Today, laminating glass is a process that involves bonding two layers of annealed glass with an inter-layer of thermoplastic. (Annealed glass is simply glass that has been cooled slowly to reduce and relieve its internal stress.) The plastic bonding agent generally used to make laminated glass is polyvinyl butyral, but other agents such as ethyl vinyl acetate or thermoplastic polyurethane are often used as well. is used to adhere a thermoplastic layer between two layers of strong glass. Some laminated glass is covered with an additional layer of resin to increase the strength of the glass.
After two pieces of glass have been attached and adhered to one another with this plastic layer and bonding agent, they are put through rollers which push the glass closer together to eliminate any air bubbles or areas without contact. Laminated glass is stronger when made with thicker layers of glass or when made with more than one layer of thermoplastic laminate.
The process of manufacturing laminated safety glass must be done under heat and pressure, when the glass is malleable and can be manipulated properly. Due to the fact that modern laminating makes glass so strong, cutting laminated glass is difficult and can be dangerous; but repairing laminated glass can be a rather simple process involving drilling beneath the top layer of glass to the thermoplastic layer between and basically filling the crack with resin. After the resin has been hardened with ultraviolet light, the strength and transparency of the glass is restored.
How Laminated Glass Protects You
Imagine that your windshield has been hit by a rock and suddenly there is a huge spider-web crack spreading from the point of impact. If your windshield were not made of laminated glass, any of a number of far more dangerous and detrimental things could have happened. The rock could have come straight through the windshield. The glass could have broken into a million sharp pieces that might have fallen into your car and presented an even bigger risk to your safety. And if that weren’t enough, your vehicle would have a gaping hole where the windshield had been, exposing you not only to the dangers of its own broken glass, but to all the things your windshield protects you from.
Laminated glass, by being stronger and by resisting real breakage, protects you even when it has been cracked. Instead of falling to pieces immediately if presented with an impact strong enough to crack it, laminated glass holds up and remains in tact, as it was designed to do. It is for this reason that laminated glass is also used in areas where building regulations must meet hurricane-resistant construction requirements. In addition to its strength and durability, the polyvinyl butyral which binds the layers of glass together significantly blocks ultraviolet radiation and increases the sound-proof qualities of the glass.
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